There's no reason why you can't have a business line and residential services at the same address. I find that the field sales agents are less knowledgeable about issues like this. He may be thinking it would generate what is called a "blocked clearance" by the system knowing you already have active service there. Are you on Fibre or copper? If copper, the drop connecting your house to the outside network should have multiple pairs on it so one would stay dedicated for your business phone and the other could be used for residential internet/Optik TV. I recommend calling in residential sales and have them look in to it further.